Twist drill grinding machines



y 22, 1959 v J. M. BRAMHALL 3,456,392

' TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1966 4 Sheets-Sheet lINVENT R 30H N\\C.\\EL. Rnn-mqLL BY can ATTORNEYS July 22, 1969 FiledAug. 30. 1966 J. M. BRAMHALL TWIST DRILL GRINDING MACHINES 4Sheets-Sheet 2 Fla. 2 I

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Hm MA ATTQRNEY y 2, 1969 J. M. BRAMHALL 3,456,392

TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1968 4 Sheets-Sheet 5\NvEN-roR Ann: M \cunel. Bahia HQLL ATTORNEY! y 1969 J. M. BRAMHALL.3,456,392

TWIST DRILL GRINDING MACHINES Filed Aug. 30. 1966 4 Sheets-Sheet 4 MumNM'QQ'EZI QEMHM BY ML (MA MAL ATTORNEY United States ,Patent Office3,456,392 Patented July 22, 1969 3,456,392 TWIST DRILL GRINDING MACHINESJohn Michael Bramhall, Grindelford, England, assignor to The SheflieldTwist Drill & Steel Co. Limited Filed Aug. 30, 1966, Ser. No. 576,041Int. Cl. B24b 19/02 US. Cl. 51-101 3 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a machine for grinding twist drills and hasfor its main object to provide a machine for grinding each flank of acentre point, split point or crankshaft drill in a single operation.

According to the invention the machine comprises a supporting base, agrinding wheel assembly mounted on said base, a drill holder unitmounted on said base for moving a drill to be ground into engagementwith the grinding wheel, a template and follower associated with saiddrill holder unit for controlling the movements of the drill holder tocorrectly position the point of the drill relative to the grinding wheelduring the grinding of the drill.

In order that the invention may be more clearly understood oneparticular embodiment thereof will now be described, by way of example,with reference to the accompanying drawings in which:

FIGURE 1 is a plan view of the machine according to the invention,

FIGURE 2 is a side elevation thereof,

FIGURE 3 is a front elevation of the machine with parts removed for thesake of clearer illustration.

FIGURES 4 and 5 are a top plan and side elevation respectively of thedrill holder shown on an enlarged scale,

FIGURE 6 is a side elevation of a detail,

FIGURE 7 is a plan view of a grinding wheel dressing device for use inconjunction with the machine, and

FIGURE 8 is a plan view of the tip or point of a centre point drill onan enlarged scale.

Referring to these drawings the machine is mounted on a supporting baseor housing A and comprises a grinding wheel assembly indicated generallyat B; a drill holder unit, indicated generally at C; and a follower unitindicated generally at D.

The drill holder unit C comprises an arm 1 rotatably mounted on a shaft2 which is slidably mounted at its ends in suitable Support bearings 6and 7, whereby the unit can be swung as a whole angularly about the axisof shaft 2 in an are indicated by the chain dotted line in FIGURE 2 andmoved laterally as indicated by the double arrow in FIGURES l and 3. Thedrill holder unit C is retained in its inward or operative position (asillustrated in the drawings) by means of a weight (not shown) attachedto one end of and suspended from a cable 3 which passes over a guidepulley 4 and is secured at its other end to said drill holder unit. Thedrill holder unit can be swung into its outward or inoperative positionby means of a handle 1a and can be retained in said outward orinoperative position by means of a retaining catch 5a, 5b.

The shaft 2, and consequently the drill holder unit as a whole, islaterally or axially adjustable by rotation of a hand wheel 8, which isin screw threaded engagement with the shaft 2 in known manner, and suchlateral or axial adjustment is limited by an axially adjustable screwstop 9.

At the upper end of the arm 1 of the drill holder unit is a cylindricalbearing or trunnion 10 in which is rotatably mounted a shaft 11 which,at the end adjacent to a grinding wheel 31, carries the drill holder andat its opposite end adjacent to the follower unit D carries aninterchangeable template 12.

The drill holder (FIGURES 4 and 5) is fixedly mounted on the end of theshaft 11 by means of a bracket mounting 13 and is thus swingable aboutthe shaft axis to move the drill 23 towards and away from the grindingwheel 31. The drill holder comprises a carrier bar 14 which at one endcarries a tail stock 18, slidable on said bar and adapted to be lockedin any adjusted position axially of the bar by means of a clamping means21. Fixedly mounted on said bar 14 intermediate the ends thereof is adrill chuck 19 which comprises a pair of pivoted clamping jaws 22 forclamping the drill 23 on the drill holder unit. The drill 23 is rigidlyheld in position on the drill holder between an axially adjustable feedscrew on the tail stock 18 and the clamping jaws 22 of the chuck 19. theclamping jaws engaging the drill on each side of each of the helicallands of the drill, the clamping jaws being held in clamped position byclamping means 24. The carrier bar 14 is slidable in a bracket mounting13 and in a block 13a, securely mounted in said bracket, and saidcarrier bar and block are adjustable angularly relative to the axis ofshaft 11 about a pivot axis 15 and lockable in adjusted position by aset screw 16 which passes through an arcuate slot 17 in said bracket.

In operation the surface of the point of the drill which is to be groundmust be in the same plane as the edge of the template 12, i.e. in theplane indicated by the chain dotted line a in FIGURES l and 5, thus theamount by which the point of the drill projects from the clamping jaws22 will vary for drills of different diameters. In order to compensatefor this variation, i.e. to compensate for the variation in the flutespiral of different diameter drills, the carrier bar 14 islongitudinally adjustable relative to the block 13a by means of anadjusting hand wheel 13b, a setting scale 130 being provided on theblock 13a for different drill diameters.

The follower-unit D (see FIGURES 1 and 6) comprises a shaft 25 axiallyadjustable in a fixed mounting 26 by means of adjusting hand wheel 27and is held in adjusted position by a clamping means 29. The shaft 25 isprovided at its projecting end with a follower 28 having an arcuatesurface which engages the template 12.

The grinding wheel assembly B comprises a suitable motor 30 on thedriving shaft of which is keyed a grinding wheel 31 the axis of which isset at an angle of from 2 to 10 to the drill point axis (see FIGURE 3)in order to generate the necessary clearance to the chisel edge of thedrill when grinding as hereinafter described.

The grinding wheel 31 and the arcuate surface of the follower 28 whichabuts the template during grinding of the drill, must be of the same, orsubstantially the same, radius and correctly positioned relative to eachother. This is ensured by a grinding wheel dressing device illustratedin FIGURE 7. This device comprises a dressing bar 32 adapted to beclamped to the drill holder unit C by means of a clamp 33 with one endof said bar positioned opposite to the grinding wheel 31 and the otherend opposite to the follower 28, The end of the bar opposite to thegrinding wheel carries a pointed diamond 34 for dressing the grindingwheel, whilst the opposite end of the bar is provided with a sharp edge35 which is arranged to abut the follower 28. In use the drill holderunit is swung outwardly, that is away from the grinding wheel andfollower, by means of the handle 10, and the dressholder unit C is thenswung back to bring the sharp edge 35 of the bar into contact with thefollower 2'8 and the follower is then retracted by the screw adjustmentmeans 26 until the diamond point 34 contacts the periphery of thegrindnig wheel 31 thus correlating the diamond point with the follower.The driving wheel motor 30 is then started and the grinding wheeldressed by traversing the drill holder unit C by means of the hand wheel8, the diamond point thus being moved across the periphery or grindingsurface of the wheel. After the grinding wheel has been dressed thedressing bar is removed from the drill holder unit. The machine is thusready for carrying out the operation of grinding a drill.

The operation of the machine will now be described when used forgrinding a centre point drill (illustrated in FIGURE 8) of which theprimary clearance 36, secondary clearance 37, the chisel edge 38, and anincreased clearance 39 adjacent the chisel edge are to be ground.

A template 12, having a shape suitable for use in grinding a centrepoint drill, is correctly positioned on shaft 11 and the drill mountedin the drill holder as above described. The drill point is thenpositioned correctly relative to the edge of the grinding wheel and thetemplate by suitable axial adjustment of the drill holder by means ofthe adjusting hand wheel 8, the position of the limit stop 9 havingfirst been correctly adjusted. The point of the drill to be ground isthen correctly positioned relative to the grinding wheel by adjustmentof the drill chuck 19, according to the diameter of the drill indicatedon the scale 130, as above described. The drill holder is then pivotedmanually about the axis of shaft 11 to bring the flank of the drillpoint to be ground into contact with the grinding wheel 31 and thetemplate 12 into contact with the follower 28. As the drill holder isrotated about the axis of shaft 11 to bring one flank of the drill pointinto contact with the grinding wheel, the template 12 causes movement ofthe drill holder unit as a whole and consequently the drill holder also,about the axis of shaft 2 towards and away from the grinding wheel, butmanual rotation of the drill holder keeps the drill point in contactwith the grinding wheel. The effect of this is that first the secondaryclearance 37 (see FIGURE 8) of the drill is ground and simultaneouslythe increased clearance 39 adjacent the chisel edge 38 is generated.Continned pivotal movement of the drill holder causes the template 12 toact on the follower 28 in such a way as to bring the primary clearance36 into engagement with the grinding wheel whereupon said primaryclearance and the chisel edge 39 are ground, During the grinding of oneflank of the drill the drill is advanced periodically by means of thetail stock feed screw 20 until the flank of the drill is correctlyground. The clamping jaws 22 of the chuck 19 are then released and thedrill turned to bring the other flank of the drill into position forgrinding the drill, the clamping jaws 22 are then again clamped and theabove described operation repeated to grind the other flank of thedrill.

It must be understood that the invention is not limited to theparticular embodiment herein described and illus- 'trated, but may bemodified in" various ways without departing from the scope of theinvention as defined in the appended claims. For example the holder unitC need not be necessarily held in its operative position by means of aweight, but the pivot arm 1 may be arranged an an angle of say 45 sothat'the holder unit tends to pivot into the operative position underits own weight. Furthermore the holder unit need not be pivotallymovable as described to move the drill holder towards the grinding wheelassembly but may be slidably movable towards and away from the grindingwheel assembly.

What is claimed is: 7

1. A machine for grinding twist drills comprising a.

supporting base, a grinding wheel assembly mounted on said base, a'drillholder unit comprising a rotatable shaft, a drill holder mounted on saidshaft, a template mounted on said shaft, said drill holder unit beingmovably mounted on said base to move the template into engagement with afollower fixedly mounted on said base and to move the drill holder andthe drill towards the grinding wheel, said drill holder being pivotableabout the axis of said rotatable shaft to move the point of the drillinto engagement with said grinding wheel, said drill holder comprising acarrier bar mounted on one end of said rotatable shaft, a drill chuckfixedly mounted on said carrier bar and a tail stock slidably mounted onsaid carrier bar, the drill being held by said drill chuck and said tailstock, and wherein said carrier bar is slidable for longitudinaladjustment in a bracket fixed to said rotatable shaft and said bracketis adjustable to effect angular adjustment of the carrier bar relativeto said rotatable shaft.

2. A machine according to claim 1, wherein said follower is mounted onone end of an axially adjustable shaft and means are provided forclamping said shaft in any axially adjusted position.

3. A machine according to claim 1, wherein the axis of the driving shaftof the grinding wheel is set at an angle to the drill point axis.

References Cited UNITED STATES PATENTS ROBERT c. RIORDON, PrimaryExaminer D. G. KELLY, Assistant Examiner I 'U.S. c1. X.R. 51- 219

